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1
Ratios of Separated Response Functions
from Pion Electroproduction
at
and

• Motivation
• Analysis
• Results
• Summary

Cornel Butuceanu
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Hall C Collaboration Meeting,
JLab, January 31, 2009
ccbutu_at_jlab.org
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Jefferson Lab Fp Collaboration

• R. Ent, D. Gaskell, M.K. Jones, D. Mack, D.
  Meekins, J. Roche, G. Smith, W. Vulcan,
• G. Warren, S.A. Wood
• Jefferson Lab, Newport News, VA , USA
• C. Butuceanu, E.J. Brash, G.M. Huber, V.
  Kovaltchouk, G.J. Lolos, S. Vidakovic, C. Xu
• University of Regina, Regina, SK, Canada
• H. Blok, V. Tvaskis
• Vrije Universiteit, Amsterdam, Netherlands
• E. Beise, H. Breuer, C.C. Chang, T. Horn, P.
  King, J. Liu, P.G. Roos
• University of Maryland, College Park, MD, USA
• W. Boeglin, P. Markowitz, J. Reinhold
• Florida International University, FL, USA
• J. Arrington, R. Holt, D. Potterveld, P. Reimer,
  X. Zheng
• Argonne National Laboratory, Argonne, IL, USA
• H. Mkrtchyan, V. Tadevosyan
• Yerevan Physics Institute, Yerevan, Armenia
• S. Jin, W. Kim
• Kyungook National University, Taegu, Korea
• M.E. Christy, C. Keppel, L.G. Tang
• Hampton University, Hampton, VA, USA

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Motivation
reactions
q

• Testing the t-pole dominance key factor in
• the extraction of the pion form factor .
• Pion electroproduction can proceed
• via isovector and isoscalar photons.
• The experimental ratio
  evolution with
• -t gives a good indication of the presence of
  isoscalar processes.
• Separated ratios and tests the t-pole
  contribution to .

t-pole
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Previous Studies

• At low -t

• At high -t

A. Nachmann, Nucl. Phys. B 115 (1976) 61
Unseparated cross section ratios
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Kinematics Coverage L/T Separation Technique
Take data at three angles ?pq0o, 4o, -4o.
Diamond cuts define common (W,Q2) coverage at
both e.
Extract sL by simultaneous fit of L,T,LT,TT
using measured azimuthal angle (fp) and
knowledge of photon polarization (e).
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Event selection
Electron-pion coincidences
Pions detected in HMS Cerenkov Coincidence
time for PID
Electrons detected in SOS Cerenkov Lead Glass
Calorimeter
Random coincidences
Exclusivity assured via 0.875ltMMlt1.05 GeV cut
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Collimator Pion Punch Through in SIMC
Simulated Missing Mass spectrum was improved by
implementing pions that were penetrating the HMS
collimator.
Pion Punchthrough Implementation resulted in an
overall improved simulated kinematic variables
(W,Q2,-t).
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Magnetic Spectrometer Calibrations
Data Analysis

• - Over-constrained p(e,ep) and elastic e
  12C reactions were
• used to calibrate spectrometer acceptances,
  momenta and
• angular offsets.
• - SOS HMS Delta/xpfp correlations were
  corrected with a
• linear dependent function of form
  .

• Corrections to the high rate data set

data were taken at high rates while
data were taken at low rates. Understanding
the rate dependent corrections was very
important with respect to the final
ratios. -New high rate tracking algorithm.
-Improved high rate tracking efficiencies
(2-9). - HMS Cerenkov blocking
correction (2-18). -High current ( data
set) target boiling correction (2-13).
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Tracking Efficiency For High Rate Data

• Tracking Efficiency as defined for Fpi2 data
  fails for Fpi1 high
• rate data (pi-).

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Tracking Efficiencies For High Rate Data

• A 8 correction to the tracking efficiencies at
  1.4MHz was
• applied to the Fpi1 high rate data (pi-).

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Target Boiling Corrections
Hydrogen
Deuterium

• Hydrogen had a boiling effect of 11 at 100
  microA.

• Deuterium had a boiling effect of 13.5 at 100
  microA.

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Fpi2 Pion Absorption and Beta efficiency
Beta gt .925
Pi- data
Pi data

• The thick HMS exit window and the addition of
  the aerogel Cherenkov resulted in an improved
  overall pion transmission.

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Fpi1 Beta Cut
Random coincidences
Real coincidences
b gt .95
beta cut
protons
p- data
p data

• A tight beta cut was applied to remove protons
  from the p data sample.
• No Aerogel used in Fpi1 experiment.

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Error Analysis

• Spectrometers well-understood after careful
  comparison with MC simulations.
• Beam energy and spectrometer
• momenta determined to lt0.1.
• Spectrometer angles to 0.5 mr.
• Agreement with published pe
• elastics cross sections lt2.
• Per data t-bin
• Typical statistical error per bin 1-2.
• Uncorrelated syst. unc. in ?UNS
• common to all t-bins 1.8(1.9).
• Additional uncorrelated unc. also
• uncorrelated in t 1.1(0.9).
• Total correlated uncertainty 3.5.
• Uncorrelated uncertainties in ?UNS are amplified
  by 1/?e in L-T separation.
• Scale uncertainty propagates directly into
  separated cross section.

Systematic Uncertainty Source e-uncorrelated common to all t-bins Pt-Pt e-random t-random Scale e-global t-global
Spectrometer Acceptance 0.6 1.0(0.6) 1.0
Radiative Corrections 0.4 0.1 2.0
Pion Absorption Correction 0.1 - 2.0
Pion Decay Correction - 0.03 1.0
MC Model Dependence 1.1(1.3) 0.2 -
Kinematic Offsets 1.0 0.2 -
HMS Tracking 0.4 0.1 1.0
Integrated Beam Charge 0.3 - 0.5
Target Thickness 0.2 - 0.8
Detection Efficiency 0.3 - 0.5
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VGL Regge Model

• Pion electroproduction in terms of exchange of p
  and ? Regge trajectories.
• - exchanged of a series of particles
• compared to a single particle.
• Model parameters fixed from pion photoproduction.
• Free parameters ?p2 and ??2 (trajectory
  cutoffs).
• ? exchange does not
• significantly influence sL at small t.

Vanderhaeghen, Guidal, Laget, PRC 57(1998)1454
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Separated Response Functions
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Separated Response Functions Ratios
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Summary

• Separated cross
  sections were extracted using
• Rosenbluth L/T separation technique.
• Ratios were extracted as a
  function of -t.
• Preliminary results show that is consistent
  with 1 over the whole
• range in t indicating a dominance of
  isovector processes at low t in the longitudinal
  response function .
• These findings confirm the expectation that
  is indeed dominated by
• the t-pole term.
• In the kinematic region studied here both ratios
  and present a
• very slight dependence of .
• The evolution of with t shows a rapid fall
  off which is consistent
• with earlier theoretical predictions,
  expected to approach ¼, the square
• of the ratio of the quark charges involved.

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HMS Cerenkov Blocking
Using data taken with open trigger (el.
pions). The TDC time window in Fpi1 is 23 larger
than in Fpi2. Use the Fpi2 data to fit the
effective gate (same CC cut). For npelt2.0 gate
width 190 ns. Implies a larger correction in
Fpi1 (18-20 at 1MHz). Significant impact in pi-
(high rate) data.
HMS CC TDC spectrum for e as identified by the
HMS CC ADC
Backup slide 1
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31, 2009
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Beta Cut Corrections
Random coincidences
Real Coincidences
Slow pions
Included in the pion absorption correction
Backup Slide 2
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31, 2009
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SOS Q3 Corrections
Low momentum (lt1.6 GeV/c) old settings
corrections works fine. High momentum (gt1.6
GeV/c) use of new SOS optic matrix new
delta/xpfp correction.
Backup Slide 3
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31, 2009
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HMS Cerenkov Blocking

• Used data taken with open trigger (el. pions)
  to fit the effective time window.
• The TDC time window in Fpi1 is 23 larger than
  in Fpi2.
• Used the Fpi2 data to fit the effective TDC gate
  (for the same CC cut used in Fpi1).
• For a CC cut of npelt1.5 the effective TDC gate
  for Fpi1 set is 184 ns.
• Implies a larger correction for Fpi1 data
  (18-20 at 1MHz).
• Significant impact in pi- (high rate) data.

HMS CC TDC spectrum for e as identified by the
HMS CC ADC

• Uncertainties associated with this correction
  are of the order of 1.6 at 1MHz.

Backup Slide 4
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31, 2009
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HMS Q3 corrections

• Using central HMS kinematics and detected proton
  momentum we reconstruct the invariant mass W
  (electron mass).

• The W vs X distribution was fitted with 1
  degree polynomial for each.

Backup Slide 5
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31, 2009
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Deuterium Corrections Uncertainties
Source Size of the correction () e-uncorrelated common to all t-bins () Pt-to-Pt e-random t-random () Scale e-global t-global ()
Beta Cut 3 3.5 0.5 - 0.5
Missing Mass 1 - 2 0.2 - 1.5
Cherenkov Block. 2 - 15 0.5 - 1.5
Target Boiling 2 - 13.5 0.2 - 1.6
Tracking Eff. 1 13.5 0.4 - 1.0
Backup Slide 6
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31, 2009
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Uncertainties Associated with Applied Corrections
Backup Slide 6
Hall C Collaboration Meeting, JLab, January
31, 2009
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